feat: persistent metadata panel, symmetric sidebar toggles, keyboard nav scroll

- Right sidebar stays open by default and shows an empty state when
  nothing is selected, instead of auto-hiding on deselect.
- Both sidebars now have a collapse button in their header and an
  expand button in the TopBar that only appears when collapsed, so
  each panel has a discoverable affordance in either state.
- Arrow-key navigation auto-scrolls the destination row into view
  with a ~35% peek margin, cueing the user that there's more content
  in the scroll direction.
- Fix: the width sentinel's measurement effect never installed its
  ResizeObserver when Timeline first rendered the loading state (ref
  was null, empty-dep effect didn't re-run), so containerWidth stuck
  at 0 and the grid fell back to 4 columns × 200px forever. Switched
  to a callback ref that attaches the observer the moment the
  sentinel actually mounts.
- KeyboardHints surface the Tab (library) and I (info) shortcuts.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/App.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useState } from 'react'
+import { useState } from 'react'
 import { Timeline } from './components/timeline/Timeline'
 import { LeftSidebar } from './components/layout/LeftSidebar'
 import { RightSidebar } from './components/layout/RightSidebar'
@@ -18,9 +18,8 @@ import { usePhotosQuery } from './hooks/usePhotosQuery'
 
 function App() {
   const [leftSidebarOpen, setLeftSidebarOpen] = useState(true)
-  const [rightSidebarOpen, setRightSidebarOpen] = useState(false)
+  const [rightSidebarOpen, setRightSidebarOpen] = useState(true)
   const [settingsOpen, setSettingsOpen] = useState(false)
-  const selectedPhotos = usePhotoStore((state) => state.selectedPhotos)
   const viewMode = usePhotoStore((state) => state.viewMode)
 
   // Bidirectional sync of filter store with URL query params.
@@ -38,24 +37,19 @@ function App() {
     getFirstPhotoId: () => allPhotos?.[0]?.id ?? null,
   })
 
-  // Auto-show right sidebar when photos are selected — but only in grid mode,
+  // Right sidebar stays open by default and shows whatever's selected
-  // so leaving the preview doesn't fight the user's prior sidebar state.
+  // (or an empty state if nothing is). User can still toggle it manually.
-  // Lives in an effect (not the render body) to avoid setState-during-render
-  // and the cascading re-renders the audit caught.
-  useEffect(() => {
-    if (viewMode !== 'grid') return
-    if (selectedPhotos.length > 0 && !rightSidebarOpen) {
-      setRightSidebarOpen(true)
-    } else if (selectedPhotos.length === 0 && rightSidebarOpen) {
-      setRightSidebarOpen(false)
-    }
-  }, [viewMode, selectedPhotos.length, rightSidebarOpen])
-
   const showRightSidebar = rightSidebarOpen && viewMode === 'grid'
 
   return (
     <div className="flex flex-col h-screen bg-bg text-text">
-      <TopBar onOpenSettings={() => setSettingsOpen(true)} />
+      <TopBar
+        onOpenSettings={() => setSettingsOpen(true)}
+        leftSidebarOpen={leftSidebarOpen}
+        rightSidebarOpen={showRightSidebar}
+        onExpandLeft={() => setLeftSidebarOpen(true)}
+        onExpandRight={() => setRightSidebarOpen(true)}
+      />
 
       <div className="flex flex-1 overflow-hidden">
         {/* Left Sidebar */}
@@ -64,7 +58,7 @@ function App() {
             leftSidebarOpen ? 'w-64' : 'w-0'
           } overflow-hidden border-r border-border bg-surface`}
         >
-          <LeftSidebar />
+          <LeftSidebar onCollapse={() => setLeftSidebarOpen(false)} />
         </div>
 
         {/* Main column — filter bar, discard bar, timeline. Lives to the
@@ -90,7 +84,7 @@ function App() {
             showRightSidebar ? 'w-80' : 'w-0'
           } overflow-hidden border-l border-border bg-surface`}
         >
-          <RightSidebar />
+          <RightSidebar onCollapse={() => setRightSidebarOpen(false)} />
         </div>
       </div>
 

frontend/src/components/KeyboardHints.tsx

@@ -14,13 +14,14 @@ export function KeyboardHints() {
         { key: 'P', action: 'Pick → heap' },
         { key: 'X', action: 'Discard' },
         { key: 'Space', action: 'Preview' },
+        { key: 'I', action: 'Info panel' },
         { key: 'Esc', action: 'Deselect' },
       ]
     : [
         { key: '↑↓←→', action: 'Navigate' },
-        { key: 'Click', action: 'Select' },
-        { key: 'Shift+Click', action: 'Range' },
         { key: 'Space', action: 'Preview' },
+        { key: 'Tab', action: 'Library panel' },
+        { key: 'I', action: 'Info panel' },
         { key: '/', action: 'Search' },
       ]
 

frontend/src/components/layout/LeftSidebar.tsx

@@ -14,6 +14,7 @@ import {
   Layers2,
   MoreHorizontal,
   Pencil,
+  PanelLeftClose,
 } from 'lucide-react'
 import clsx from 'clsx'
 import { sourceFolders, library, photos as photosApi, type FolderTreeNode } from '../../services/api'
@@ -41,7 +42,11 @@ interface TreeItem {
   type?: 'folder' | 'heap' | 'special'
 }
 
-export function LeftSidebar() {
+interface LeftSidebarProps {
+  onCollapse: () => void
+}
+
+export function LeftSidebar({ onCollapse }: LeftSidebarProps) {
   const [expandedItems, setExpandedItems] = useState<Set<string>>(new Set(['library', 'folders', 'heaps']))
   const [isScanning, setIsScanning] = useState(false)
   // Inline rename state for source-root rows. Stores the id being edited
@@ -674,6 +679,19 @@ export function LeftSidebar() {
 
   return (
     <div className="flex h-full flex-col bg-surface">
+      {/* Header with collapse button. Matches the right sidebar header
+       *  so both panels have symmetric affordances. */}
+      <div className="flex h-11 flex-shrink-0 items-center justify-between border-b border-border px-4">
+        <h2 className="text-sm font-semibold text-text">Library</h2>
+        <button
+          onClick={onCollapse}
+          className="rounded p-1 text-text-muted hover:bg-surface-2 hover:text-text"
+          title="Collapse panel (Tab)"
+          aria-label="Collapse panel"
+        >
+          <PanelLeftClose className="h-4 w-4" />
+        </button>
+      </div>
       {/* Tree View */}
       <div className="flex-1 overflow-y-auto py-2">
         {libraryTree.map((item) => renderTreeItem(item))}

frontend/src/components/layout/RightSidebar.tsx

@@ -1,5 +1,5 @@
 import { useState } from 'react'
-import { X, Star, Info, ShoppingBasket, Trash2, Plus } from 'lucide-react'
+import { X, Star, Info, ShoppingBasket, Trash2, Plus, PanelRightClose } from 'lucide-react'
 import clsx from 'clsx'
 import { useMutation, useQueryClient } from '@tanstack/react-query'
 import { usePhotoStore } from '../../store/photoStore'
@@ -21,7 +21,11 @@ import { COLOR_LABEL_OPTIONS } from '../../constants/colorLabels'
  *  - 2+ photos selected → renders a slim bulk-action panel that fans out
  *    rating / color / discard / pick across the entire selection.
  */
-export function RightSidebar() {
+interface RightSidebarProps {
+  onCollapse: () => void
+}
+
+export function RightSidebar({ onCollapse }: RightSidebarProps) {
   const { selectedPhotos, activePhotoId, clearSelection } = usePhotoStore()
   const queryClient = useQueryClient()
 
@@ -134,12 +138,51 @@ export function RightSidebar() {
     },
   })
 
+  // Unified header rendered in every branch so the collapse button is
+  // always reachable regardless of selection state. Title and the
+  // clear-selection X adapt to what's selected.
+  const headerTitle =
+    selectedPhotos.length === 0
+      ? 'Metadata'
+      : selectedPhotos.length === 1
+        ? 'Metadata'
+        : `${selectedPhotos.length} Photos Selected`
+
+  const Header = () => (
+    <div className="flex h-11 flex-shrink-0 items-center justify-between border-b border-border px-4">
+      <h2 className="text-sm font-semibold text-text">{headerTitle}</h2>
+      <div className="flex items-center gap-1">
+        {selectedPhotos.length > 0 && (
+          <button
+            onClick={clearSelection}
+            className="rounded p-1 text-text-muted hover:bg-surface-2 hover:text-text"
+            title="Clear selection (Esc)"
+            aria-label="Clear selection"
+          >
+            <X className="h-4 w-4" />
+          </button>
+        )}
+        <button
+          onClick={onCollapse}
+          className="rounded p-1 text-text-muted hover:bg-surface-2 hover:text-text"
+          title="Collapse panel (I)"
+          aria-label="Collapse panel"
+        >
+          <PanelRightClose className="h-4 w-4" />
+        </button>
+      </div>
+    </div>
+  )
+
   if (selectedPhotos.length === 0) {
     return (
-      <div className="flex h-full items-center justify-center p-4 text-center">
+      <div className="flex h-full flex-col bg-surface">
-        <div className="text-text-muted">
+        <Header />
-          <Info className="mx-auto mb-2 h-8 w-8" />
+        <div className="flex flex-1 items-center justify-center p-4 text-center">
-          <p className="text-sm">Select photos to view details</p>
+          <div className="text-text-muted">
+            <Info className="mx-auto mb-2 h-8 w-8" />
+            <p className="text-sm">Select photos to view details</p>
+          </div>
         </div>
       </div>
     )
@@ -150,17 +193,7 @@ export function RightSidebar() {
     const id = activePhotoId ?? selectedPhotos[0]
     return (
       <div className="flex h-full flex-col bg-surface">
-        <div className="flex h-11 flex-shrink-0 items-center justify-between border-b border-border px-4">
+        <Header />
-          <h2 className="text-sm font-semibold text-text">Metadata</h2>
-          <button
-            onClick={clearSelection}
-            className="rounded p-1 text-text-muted hover:bg-surface-2 hover:text-text"
-            title="Clear selection"
-            aria-label="Clear selection"
-          >
-            <X className="h-4 w-4" />
-          </button>
-        </div>
         <PhotoInfoPanel photoId={id} />
       </div>
     )
@@ -171,18 +204,7 @@ export function RightSidebar() {
 
   return (
     <div className="flex h-full flex-col bg-surface">
-      <div className="flex items-center justify-between border-b border-border px-4 py-3">
+      <Header />
-        <h2 className="text-sm font-semibold text-text">
-          {selectedPhotos.length} Photos Selected
-        </h2>
-        <button
-          onClick={clearSelection}
-          className="rounded p-1 text-text-muted hover:bg-surface-2 hover:text-text"
-          title="Clear selection"
-        >
-          <X className="h-4 w-4" />
-        </button>
-      </div>
 
       <div className="space-y-3 border-b border-border p-4">
         <p className="text-xs text-text-muted">

frontend/src/components/layout/TopBar.tsx

@@ -1,23 +1,59 @@
-import { Settings } from 'lucide-react'
+import { Settings, PanelLeftOpen, PanelRightOpen } from 'lucide-react'
 import muliLogo from '../../assets/muli-logo.png'
 
 interface TopBarProps {
   onOpenSettings: () => void
+  leftSidebarOpen: boolean
+  rightSidebarOpen: boolean
+  onExpandLeft: () => void
+  onExpandRight: () => void
 }
 
 /**
  * Slim top bar — logo on the left, settings gear on the right. The
  * active heap badge moved into the Heaps panel in the left sidebar
  * (where it actually relates to the heap rows the user navigates to).
+ *
+ * Also hosts the "expand sidebar" affordances: when a side panel is
+ * collapsed, a small panel-open icon appears on the corresponding edge
+ * so the user has a way to bring it back without hunting for the
+ * keyboard shortcut. When the panel is open, the button hides — its
+ * collapse twin lives in the panel's own header.
  */
-export function TopBar({ onOpenSettings }: TopBarProps) {
+export function TopBar({
+  onOpenSettings,
+  leftSidebarOpen,
+  rightSidebarOpen,
+  onExpandLeft,
+  onExpandRight,
+}: TopBarProps) {
   return (
     <header className="flex h-12 items-center justify-between border-b border-border bg-surface px-4">
       <div className="flex items-center gap-2">
+        {!leftSidebarOpen && (
+          <button
+            onClick={onExpandLeft}
+            className="rounded p-1.5 text-text-muted transition-colors hover:bg-surface-2 hover:text-text"
+            title="Expand panel (Tab)"
+            aria-label="Expand left panel"
+          >
+            <PanelLeftOpen className="h-4 w-4" />
+          </button>
+        )}
         <img src={muliLogo} alt="Mulimago" className="h-7 w-7 object-contain" />
         <h1 className="text-lg font-semibold text-text">Mulimago</h1>
       </div>
       <div className="flex items-center gap-2">
+        {!rightSidebarOpen && (
+          <button
+            onClick={onExpandRight}
+            className="rounded p-1.5 text-text-muted transition-colors hover:bg-surface-2 hover:text-text"
+            title="Expand panel (I)"
+            aria-label="Expand right panel"
+          >
+            <PanelRightOpen className="h-4 w-4" />
+          </button>
+        )}
         <button
           onClick={onOpenSettings}
           className="rounded p-1.5 text-text-muted transition-colors hover:bg-surface-2 hover:text-text"

frontend/src/components/timeline/Timeline.tsx

@@ -1,4 +1,4 @@
-import { useRef, useEffect, useMemo, useState } from 'react'
+import { useRef, useEffect, useMemo, useState, useCallback } from 'react'
 import { useVirtualizer } from '@tanstack/react-virtual'
 import { format, parseISO } from 'date-fns'
 import { usePhotoStore } from '../../store/photoStore'
@@ -167,7 +167,6 @@ export function Timeline() {
   // because parentRef has padding and we'd otherwise have to subtract
   // it (and account for any scrollbar) — easy to get wrong by a pixel
   // and end up with a column count off by one.
-  const widthSentinelRef = useRef<HTMLDivElement>(null)
   const [containerWidth, setContainerWidth] = useState(0)
 
   const {
@@ -295,17 +294,35 @@ export function Timeline() {
   // resize, and any layout change driven by the sidebar collapse /
   // right panel toggle. ResizeObserver picks up everything window
   // resize misses (sidebar collapse doesn't fire window resize).
-  useEffect(() => {
+  //
-    const el = widthSentinelRef.current
+  // Uses a callback ref (not useRef + useEffect) because Timeline
+  // early-returns a loading/empty state before the sentinel exists,
+  // so a mount-only effect would see a null ref and never install
+  // the observer. The callback ref fires whenever the sentinel
+  // actually attaches, which is the moment we can measure it.
+  const roRef = useRef<ResizeObserver | null>(null)
+  const measureElRef = useRef<HTMLDivElement | null>(null)
+  const widthSentinelRef = useCallback((el: HTMLDivElement | null) => {
+    roRef.current?.disconnect()
+    roRef.current = null
+    measureElRef.current = el
     if (!el) return
     const measure = () => setContainerWidth(el.clientWidth)
     measure()
     const ro = new ResizeObserver(measure)
     ro.observe(el)
-    window.addEventListener('resize', measure)
+    roRef.current = ro
+  }, [])
+  useEffect(() => {
+    const onResize = () => {
+      const el = measureElRef.current
+      if (el) setContainerWidth(el.clientWidth)
+    }
+    window.addEventListener('resize', onResize)
     return () => {
-      ro.disconnect()
+      window.removeEventListener('resize', onResize)
-      window.removeEventListener('resize', measure)
+      roRef.current?.disconnect()
+      roRef.current = null
     }
   }, [])
 
@@ -318,6 +335,17 @@ export function Timeline() {
     [items]
   )
 
+  // Parallel array: photoRows[i] corresponds to items[photoRowItemIndex[i]].
+  // Lets keyboard nav jump the virtualizer to the destination row even when
+  // it hasn't been rendered yet (beyond the overscan window).
+  const photoRowItemIndex = useMemo(() => {
+    const map: number[] = []
+    items.forEach((it, idx) => {
+      if (it.type === 'row') map.push(idx)
+    })
+    return map
+  }, [items])
+
   // Flat visible-order id sequence — exactly the order the user reads
   // off the grid (top-to-bottom, left-to-right within each row).
   // Includes duplicates from tag-grouping; landing on the same photo's
@@ -416,6 +444,35 @@ export function Timeline() {
         } else {
           selectPhoto(dest.photo.id)
         }
+        // Bring the destination row into view if it's off-screen, leaving
+        // a "peek" margin so the next row above/below stays partly visible
+        // — cues the user that there's more content in the scroll direction.
+        // In-viewport moves are a no-op, so same-row arrow presses don't
+        // jitter the scroll position.
+        const itemIdx = photoRowItemIndex[nextRow]
+        const scrollEl = parentRef.current
+        if (itemIdx !== undefined && scrollEl) {
+          // Sum item heights up to itemIdx to get this row's offset in the
+          // virtualizer's coordinate space. Cheap enough at O(items) and
+          // avoids reaching into virtualizer.measurementsCache internals.
+          let rowTop = 0
+          for (let i = 0; i < itemIdx; i++) rowTop += items[i].height
+          const rowHeight = items[itemIdx].height
+          const peek = Math.round(cellSize * 0.35)
+          const viewTop = scrollEl.scrollTop
+          const viewBottom = viewTop + scrollEl.clientHeight
+          if (rowTop - peek < viewTop) {
+            // Destination is above (or flush with) the viewport top. Leave
+            // `peek` pixels of the previous row visible above it.
+            scrollEl.scrollTo({ top: Math.max(0, rowTop - peek) })
+          } else if (rowTop + rowHeight + peek > viewBottom) {
+            // Destination is below the viewport bottom. Leave `peek` pixels
+            // of the next row visible below it.
+            scrollEl.scrollTo({
+              top: rowTop + rowHeight + peek - scrollEl.clientHeight,
+            })
+          }
+        }
       }
 
       switch (e.key) {
@@ -455,7 +512,7 @@ export function Timeline() {
     window.addEventListener('keydown', handleKeyDown)
     return () => window.removeEventListener('keydown', handleKeyDown)
     // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [viewMode, photoRows, photos, selectedPhotos, activePhotoId])
+  }, [viewMode, photoRows, photos, selectedPhotos, activePhotoId, photoRowItemIndex, items, cellSize])
 
   if (isLoading) {
     return (